Aiming at the problem that the traditional subspace-like direction finding algorithm fails in underdetermined scenarios and requires the number of signal sources as a priori information, a GNSS spoofing source direction finding method based on coprime array is proposed to improve the application security of satellite navigation receivers in spoofing environment. Specifically, we first construct the cyclic correlation matrix to reduce the impact of noise on the performance of the coprime array signal processing, and the virtual domain equivalent array signal is obtained by vectoring the cyclic correlation matrix. On this basis, an optimization problem based on sparse signal reconstruction in virtual domain is designed to achieve high-precision, multi-degree of freedom direction finding for sources by minimizing the fitting error. Finally, the simulation results show that compared with traditional subspace algorithm, the proposed algorithm has higher estimation accuracy, and the direction finding results are still reliable under the case of underdetermined.